Retinal Displacement Rates in Pneumatic Retinopexy Versus Pars Plana Vitrectomy For Primary Retinal Detachment

Metamorphopsia, Retinal Detachment

Patients may experience metamorphopsia, or image distortion, after having vitrectomy to repair their rhegmatogenous retinal detachments (RRDs) especially those with a detached macula. Retinal displacement, as measured on autofluorescence photography, likely contributes to this distortion. There is no study in the scientific literature comparing the rate of retinal displacement and its association with visual function, including metamorphopsia, in patients undergoing different procedures for RRD repair. Based on the recently published PIVOT trial, patients who underwent Pneumatic Retinopexy (PnR) had less vertical distortion at 12 months than patients who had Pars Plana Vitrectomy (PPV). It is hypothesized that PnR will cause less retinal displacement than PPV for patients with macula-off primary retinal detachment.

Rhegmatogenous retinal detachments (RRD) are a sight-threatening condition with an incidence of approximately 10 per 100 000 people. RRDs can be broadly classified into those with the macula still attached, and those with the macula detached. Without surgical intervention by a vitreoretinal surgeon, retinal detachment almost invariably results in permanent sight loss. Current techniques for RRD repair include scleral buckle (SB), pneumatic retinopexy (PnR), and pars plana vitrectomy (PPV) with or without combination of SB. Pneumatic retinopexy (PnR) is a minor surgical intervention employed to repair retinal detachments, carried out in the clinic's procedure room. Standard criteria for this procedure include one or more retinal breaks within one clock hour located at the superior eight clock hours, without signs of proliferative vitreoretinopathy. The procedure involves injection of a small gas bubble into the eyeball via a fine needle. Two gases can be injected into the eye: perfluoropropane (C3F8), which lasts 6 weeks, and sulfur hexafluoride (SF6), which lasts about 2 weeks. After injection of the gas bubble, the patient is required to maintain a strict 'head posture' (for example, head tilt to left) for up to 10 days. The gas bubble spontaneously dissipates after 2-6 weeks, depending on the gas selected. Additionally, laser treatment or cryotherapy is carried out either before or 1-2 days after injection of the gas bubble, to secure the retinal tear. The advantages of PnR over PPV are: (1) Low risk of cataract - secondary cataract formation is uncommon after PnR, but more common after PPV; (2) Quicker visual rehabilitation - due to the smaller size gas bubble and less invasive nature of the procedure, patients undergoing PnR commonly have improved vision within days after treatment; (3) Immediate availability of intervention - unlike PPV, PnR is carried out in a treatment room, and there are no delays due to operating room availability. Pars plana vitrectomy (PPV) is a surgical procedure carried out in the operating room under regional anesthetic, and often times sedation. During PPV, the vitreous gel is removed from the eye to allow space for a larger gas bubble than is possible in PnR, and also to relieve any vitreous traction which may otherwise impair reattachment of the retina. The retina is reattached by either draining the subretinal fluid through a peripheral retinal break; by draining the subretinal fluid through a posterior retinotomy; or by using a heavier-than-water liquid such as perfluocarbon (PFC) to push out the subretinal fluid. Laser or cryotherapy is applied around the retinal tear to create chorioretinal adhesions (as in PnR). At the end of the surgery, the vitreous cavity is filled with a substance that will tamponade the retina to the wall of the eye while the adhesions form. Tamponade agents can be temporary, such as SF6 and C3F8 (same gases as mentioned for PnR), which are absorbed by 2-6 weeks, or long term, such as silicone oil, which requires a second surgery to remove. After the surgery, the patient may be required to maintain a 'head posture' (for example, head tilt to left) for up to one week to support the area of the retinal tear optimally by 'floating' the gas bubble up against it. As the gas bubble is larger in PPV, the head posturing requirements are less strict. The advantages of PPV over PnR are: (1) higher primary single procedure success rate (although same final reattachment success rate); (2) less follow-up visits in the first week. Patients may experience metamorphopsia, or image distortion, after having their RRD repaired especially those with a detached macula. In 2010, Shiragami et al were the first to demonstrate hyperfluorescent lines, adjacent to the retinal blood vessels in Fundus autofluorescence imaging (FAF) of the retina after RD repair surgery.They theorized that these lines which are called Retinal Vessel Printings (RVP) correspond to the location of the retinal blood vessels before the retinal detachment. In FAF, an image is taken with structures that naturally fluoresce such as the lipofuscin in the retinal pigment epithelium (RPE) appearing brighter. According to this theory, prior to the retinal detachment, certain RPE cells were covered by the retinal blood vessels. Afterwards, with the displacement of the retina due to the retinal detachment these RPE cells become exposed to light which increases in metabolic activity producing more lipofuscin and therefore, appearing more hyperautofluorescent on the FAF. Moreover, these reference lines allow us to quantify the displacement of the retina after retinal detachment surgeries. In this study by Shiragami, 62.8% of eyes demonstrated hyperautofluorescent lines superior to the retinal blood vessels suggesting downward displacement. Since Shiragami's first report, several other studies looked into retinal displacement after RD repair. There is no study in the scientific literature comparing the rate of retinal displacement and its association with visual function, including metamorphopsia, in patients undergoing different procedures for RRD repair. The aim of this study is to compare retinal displacement following primary macula-off retinal detachment repair treated with pneumatic retinopexy (PnR) versus pars plana vitrectomy (PPV). The primary study hypothesis is that pneumatic retinopexy will cause less retinal displacement at 3 months for patients with macula-off primary retinal detachment.

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